Most illegal workers in the US are Mexicans who mow lawns, clean motel sheets, butcher hogs, pick strawberries, and otherwise toil away at tasks that, as George W. Bush once said, "Americans won't do." And they often are paid less than the minimum wage.

A widely held assumption in Washington's debate about immigration is that native-born Americans avoid menial and dirty work. Laid-off autoworkers wouldn't really wash dishes at a Denny's or milk cows on a dairy farm, would they? Such a notion has long helped justify a flow of foreign workers into the US – or possibly an amnesty for those hiding from the law.

Recent recessions have been short enough that jobless Americans who rely on government benefits waited for a "good job" to return. But this "Great Recession" has been long and deep. The unemployment rate has doubled from 4.7 to 9.4 percent, and it may keep rising into next year. Many layoffs appear permanent as whole industries have collapsed and new fields, such as clean energy, are slow to emerge. The percentage of Americans "mal-employed" – working below their skill or education – is higher than in recent recessions.

With people desperate for income, downward mobility may be on the way up. News reports show long lines of applicants for a janitor's job or for work at a factory after a federal raid clears out the illegal workers.

Maybe it's a myth that Americans won't take certain jobs. In fact, a study by the Center for Immigration Studies used 2005-07 data to look at 465 occupations. Only four had a majority of immigrants in them: plasterers and stucco masons, agricultural graders and sorters, personal appliance workers, and tailors and dressmakers.

In every other occupation, such as janitors, maids, and groundskeepers, a large majority were filled by native-born Americans. The report's conclusion: "The often-made argument that immigrants only take jobs Americans don't want is simply wrong."

The US job market is too dynamic to be easily segmented. Americans move too often for new jobs – more than a third live outside the state in which they were born. This recession can help bust the myth that native-born workers are too snooty to get their boots dirty in farm fields and back shops.